The broad, long-term objectives are to develop retinal transplantation models for saving or restoring retinal function and to learn more about basic principles underlying CNS and retinal development and regeneration, both of which may have clinical applications in the years ahead. Since retina-to-retina grafting is a new research field, the factors that influence graft differentiation and the extent of graft/host integration and function are poorly understood. The currently used transplantation method grafting retinal tissue aggregates - in contrast to grafting whole sheets - is inadequate because retinal grafts approaching normal organization cannot be produced. However, recent results indicate that cografting embryonic retinal pigment epithelial (RPE) cells may improve the lamination of retinal grafts. The specific aims and experiments are: (1) Test whether RPE is important for the differentiation of embryonic retinal grafts to adult retina. The influence of both host and donor RPE on retinal will be investigated. Whole sheets of matrix-embedded embryonic retina, with or without its RPE attached, will be grafted by an anterior approach to the subretinal space with or without cutting out a "window" in the host retina, and with or without the presence of host at the implantation site. Graft differentiation and integration will be evaluated using histology, immunohistochemistry, and electron microscopy. (2) Study the extent of graft/host integration by labeling grafted donor tissue to distinguish it from host tissue. Embryonic donor tissue will be labeled prior to grafting with a marker for dividing cells, eg, BrdU and 3H-thymidine, or with vital fluorescent or electron-dense dyes. 3) Study host/graft neuronal interaction using tracing techniques. Host retinal cells or graft cells will be labeled retro- or anterogradely with tracers, e.g., horseradish peroxidase or Fluorogold in vivo or in whole mounts in vitro. 4) Optimize donor tissue cryopreservation and hibernation parameters, which will be useful for future transplantation purposes; optimize the cryopreservation medium and procedure, and grafting method to obtaIn viable and differentiated grafts from long-term stored retinas.